Coral bleaching Coral reefs have recently been affected by bleaching i.e. the discoloration or loss of its symbiotic algae.

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1 The activity of the zooxanthellae also assists in the release of lime for the construction of a coral skeleton. The biggest threat to corals, apart from humans who collect them and pollute the sea, is coral bleaching. Coral bleaching Coral reefs have recently been affected by bleaching i.e. the discoloration or loss of its symbiotic algae. The cause of these widespread bleaching incidents is uncertain but recent research indicates that the cause may be unusually warm waters. The optimum temperature for coral growth is between 26 C and 27 C. Temperatures above 29 C cause the stressed coral polyps to actively expel the algae giving the coral a bleached appearance. Bleached corals have difficulty recovering; a reef can take years to recover, and subsequent bleaching incidents may make it impossible. Without their symbiotic algae, corals are unable to deposit the calcium carbonate skeleton that makes up the foundation of a coral reef. Not only corals, but also all reef organisms could potentially lose their habitat because of bleaching incidents, as the calcium carbonate structure of the reef erodes away. 16

2 JELLYFISH Ocean drifters found mainly in the open ocean, but often wash ashore. Jellies have rounded bell-shaped bodies (medusae), which contain a layer of jelly that consists of approximately 95% water. This layer varies in thickness in different jellies. They have tentacles at the open end of the bell that is armed with stinging cells. There is a square mouth with oral arms called the manubrium. They feed on small fish, shrimps and plankton e.g. fish larvae. They have very few predators of their stinging tentacles. However, they are an important source of food for some species of turtle and the ocean sunfish. Plastic bags drifting in the ocean are often mistaken for jellyfish by these animals resulting in them eating it by mistake. Some species are considered a delicacy in Japan. That the box jellyfish can give a painful sting and that it s Australian relative can kill a human being in 3 minutes. 17

3 HYDROIDS Polyps 2mm to hydroid colonies of 25cm Many of the tufts growing on rocks are hydroids and not seaweeds at all. Some hydroids are found growing on shells of snails. The hydroids protect the snail by deterring predators while the hydroids eat the scraps or waste products from the snail. This relationship is commensalism as the one organism benefits while the other organism is not harmed. Hydroids form colonies, which often look like delicate trees or feathers. Other species of hydroids are branched in an orderly and elegant fashion. The tiny polyps are borne on the branches and may be housed in small cups. The polyps can extend for feeding and can retract into the cups after feeding. Some hydroids have an external sheath or perisarc made of chitin and protein. Divers avoid hydroids as they have a fairly powerful sting. Hydroids are carnivorous and use their tentacles to catch minute shrimps, crabs, fish and eggs floating in the water. The digestive enzymes of hydroids are able to handle large prey. are nudibranchs (sea slugs), flat worms and butterfly fish. Hydroids are named after Hydra, the multiheaded goddess of Greek mythology because they multiply by budding. The Goddess grew two heads in place of every one Hercules cut off. 18

4 BLUEBOTTLES Bluebottles live on the surface of the open ocean, but are often blown ashore by onshore winds. They are unusual hydroid colonies, which consist of highly specialised individuals that are all interdependent. They prey on small fishes that they catch with their tentacles. Marine turtles and sea swallows prey on bluebottles. Plough snails and sea slugs (nudibranchs) may eat bluebottles washed ashore. Structure of the bluebottle or Portuguese man-o -war Living Shores: Figure 186 The smaller raft hydroid with a circular raft and the by-the-wind sailor with an oval raft and vertical sail are smaller colonies similar to the bluebottle. They set sail to the wind as a colony, producing a thin bright blue membrane of stiff material, orientated diagonally across the colony s body. The painful stings of a bluebottle should be washed off with salt water and are best treated with sap from the leaf of a sour fig plant or vinegar. A medical practitioner using antihistamines should treat severe cases. 19

5 Quick review 1. Identify the animals shown in the table below by giving the Phylum and the common name. Phylum: Phylum: Common name: Common name: 2. List three characteristics that all Cnidarians have in common. 3. Label the following parts on the animal below. a b 4. Name one interesting thing you would share with a visitor at the touch pool 20